The invention relates to magnetic disk apparatus, recording medium, and medium accessing method using a constant density recording system and, more particularly, to magnetic disk apparatus, recording medium, and medium accessing method which can perform high density recording by reducing the track pitch.
In association with the recent requirements large capacity, high processing speed, low price, and miniaturization of computer system, large capacity, high processing speed, low pricee, and miniaturization are also required with respect to a magnetic disk apparatus. Among them, to obtain both large capacity and small size, it is necessary to raise a recording density of a disk medium. For this purpose, a constant density recording system (hereinafter, referred to as a "CDR") in which a linear density of the information recording in the track direction is made constant is used. Further, a track pitch is reduced.
Hitherto, in a magnetic disk apparatus using the CDR, as shown in FIG. 1, a disk medium is CDR formatted. According to a disk medium 10 which has been CDR formatted, tracks formed in the circumferential direction are divided into a plurality of zones in the radial direction and a clock signal of a different frequency is used every zone, so that information is read and written at a constant linear velocity. Each track is divided into sectors in the circumferential direction by using an index 11 as a reference.
FIG. 2 shows a head mechanism to read and write disk medium 10. The disk medium 10 is rotated by a spindle motor. A head 12 is attached to an edge of a head arm 28 and is turned in the direction which traverses the tracks in the circumferential direction by a voice coil motor (hereinafter, referred to as a "VCM") 26 comprising fixed magnetic circuits 30 and movable coils 32. A write head and a read head are provided for the head 12.
Since a dead space 17 is provided between the tracks as shown in FIG. 3, a track pitch on the disk medium 10 is set to be wider than, for example, a core width W of a write head 36. The dead space 17 is used to prevent a situation such that even when the head is positioned to the center of the track, a positional deviation occurs to a certain degree by a seeking operation, a vibration from the outside, or the like, the write head 36 is projected to the adjacent track, and data is erased. A width of dead space 17 is ordinarily set to a value of about 1/5 to 1/4 of the core width W of the write head 36.
To realize the high density recording in the magnetic disk apparatus, it is sufficient to reduce the track pitch of the disk medium as much as possible. For example, a method of eliminating the dead space between the tracks is considered. However, the dead space between the tracks is provided by the following reasons and cannot be omitted.
First, a write head using a magnetic head and a smaller read head using a magnetoresistive device are provided for a recent head. In case of constructing the head by only the read head, by using the magnetoresistive device, the core width can be narrowed and even if there is no dead space, data can be read without interfering with the adjacent track. However, since the write head of a large core width is also provided for the head, the dead space cannot be eliminated.
In order to miniaturize the magnetic disk apparatus, the head positioning mechanism cannot help using the rotary type shown in FIG. 2 instead of the rectilinear type. According to the rotary type, the moving direction of the head 12 doesn't always cross the track direction on the disk medium 10 at a right angle and a certain angle exists between those directions due to the track position. At the same time, the centers of the write head and read head are deviated. Therefore, as shown in FIG. 4A, the head is positioned for the rotational center so as to position the write head 36 to a track center 37 in the writing mode. On the other hand, in the reading mode, as shown in FIG. 4B, the head is positioned so as to locate a read head 34 to the track center 37. Therefore, even in the same track, an offset has to be applied to the head positioning mechanism to rotate the rotary shaft 35 controlling the head position upon switching from the writing operation to the reading operation.
Further, according to a CDR format, an ID section in which address information or the like has been written exists before a data section as shown in each track of FIG. 5. When the data section is written, the ID section is first read and the data is subsequently written into the data section. However, since it takes a time to apply an offset to the head positioning mechanism, the ID section is read in a state without an offset as shown in FIG. 4A.
The ID section is generally written onto the disk medium only at the time of the CDR formatting which is executed upon shipping from the factory. Moreover, a large seeking operation is not also executed when the ID section is written. Therefore, no influence is exerted on the ID section of the adjacent track.
In case of using the CDR format, however, since the number of sectors of one circumference differs every zone, at the boundary between, for example, the zone Nos. 1 and 2 in FIG. 5, the ID section of the track of the zone of No. 2 comes to the position adjacent to the data section of the track of the zone of No. 1. Since the writing and reading operations are frequently executed in the data section, there is a high possibility such that an influence is exerted on the ID section of the adjacent track. For example, in the case where the head has been positioned to the track of the zone No. 1 which is in contact with the zone boundary in FIG. 5 and writing operation has been performed, the head relatively moves on the track while causing an error due to the seeking operation, vibration, or the like. Therefore, the ID section of the track of the adjacent zone No. 2 is interfered as shown in a hatched portion due to the error by the writing operation of the data section, so that an adverse influence is exerted. Because of such reasons, the dead space provided between the tracks cannot be eliminated and it is difficult to narrow the track pitch any more.